Steps to reproduce

$ pcs stonith create F1 fence_xvm
Warning: Validating resource options using the resource agent itself is enabled by default and produces warnings. In a future version, this might be changed to errors. Specify --agent-validation to switch to the future behavior.                                                                                                                                        
Warning: Validation result from agent:

However, the message exists in validation result:

$ pcs stonith create F2 fence_xvm --debug 2>&1 | grep "<pacemaker-result" -A 8
<pacemaker-result api-version="2.38" request="/usr/sbin/stonith_admin --validate --output-as xml --agent fence_xvm">
  <validate agent="fence_xvm" valid="false">
    <command code="61">
      <output source="stdout">No domain specified!
</output>
    </command>
  </validate>
  <status code="1" message="Error occurred"/>
</pacemaker-result>